This invention relates to a current amplifier circuit and a current amplifying type differential amplifier converter circuit.
Conventionally, there is a current amplifier circuit, for example, shown in FIG. 5. In operation, if bias currents flowing through transistors T.sub.6, T.sub.7 and transistors T.sub.8, T.sub.9 are represented by I, I.sub.B and I.sub.X, respectively, the base voltage of transistor T.sub.8 is given by EQU 2.multidot.(KT/q.multidot.I/I.sub.S)
where K is the Bolzmann constant, T is an absolute temperature, q is the electron charge and I.sub.S is the collector reverse saturation current. When T=300.degree. K., KT/q=2.multidot.26.multidot.10.sup.-3, and the base voltage of the transistor T.sub.8 is given by EQU 2.multidot.(26.multidot.10.sup.-3 ln I/I.sub.S)=26.multidot.10.sup.-3 .multidot.(ln I.sub.B /I.sub.S +ln I.sub.X /I) ln (I/I.sub.S).sup.2 =ln I.sub.B I.sub.X /I.sub.S.sup.2
Rearranging this equation as I.sub.B =I.sub.X /hFE, EQU I.sup.2 =I.sub.X.sup.2 /hFE EQU Then EQU I.sub.X =I.sqroot.hFE
Thus the biasing current I.sub.X flowing through transistor T.sub.8 is .sqroot.hFE times as large as the biasing current I.
The current gain is approximately hFE/2 if an input current is represented by i.
In the above circuit arrangement, the biasing current I.sub.X and the current gain are greatly dependent on hFE and influenced by variations in the elements used, so that the arrangement is difficult to design and not suitable for integration.
The object of this invention is to provide a current amplifier circuit and a current amplifying type differential current converter circuit in which the biasing current and the current gain are less dependent on hFE and not influenced by variation in the elements used.